1. Field of the Invention
The present invention relates to an automobile air conditioner, and more particularly to a temperature control device for an automobile air conditioner having a cooling unit and usable for both heating and cooling.
2. Description of the Prior Art
Heretofore, a temperature control of automatic temperature regulating type has been used with an automobile air conditioner, wherein a temperature regulating element is operated by an actuator in response to variations of three resistance values representing air temperature in the automobile and operative conditions of a temperature setting element and the temperature regulating element so as to keep a certain functional relationship among the three resistance values.
A typical automobile air conditioner has three air outlets; namely, a VENT outlet for blowing out air from a dashboard, a HEAT outlet for blowing air at the feet of persons on automobile seat, and a DEF outlet for blowing air toward a windshield. An outlet-selecting lever is provided on the dashboard, for selectively opening doors at the three outlets, i.e., a VENT door, a HEAT door, and a DEF door, so as to run the air conditioner in a corresponding mode. In the control of the automatic temperature regulating type, the aforesaid doors are automatically switched over for being opened or closed depending on the conditions in the automobile.
The automobile air conditioner of the aforesaid construction is used both for cooling and for heating. An air conditioner switch is provided for stopping the operation of a compressor of a cooling unit thereof and for keeping the cooling unit unoperated when the air conditioner is used only for heating.
As regards the temperature regulation during the operation for heating, there are two methods; namely, a method of heating the air by a heating unit after the air coming through a cooling unit, and a method of mixing the air from the cooling unit with the air from the heating unit. In either of the two methods, even if the temperature setting is fixed, there is a difference in air temperature at the outlet between the time when the cooling unit is operated and the time when the cooling unit is unoperated.
More particularly, for a given mode of operation, the air temperature at the air conditioner outlet when the compressor of the cooling unit is operated tends to be lower than that when the compressor is unoperated. The air temperature in the automobile is balanced at an intermediate point between the outside temperature and the outlet temperature of the air conditioner, where the amount of heat entering from the air conditioner into the inside of the automobile (or heat removed from the inside of the automobile) is equilibrated with the amount of heat leakage from (or into) the automobile due to conduction of the automobile body and ventilation.
Thus, the air temperature in the automobile varies as the temperature at the outlet varies. Accordingly, even if the temperature setting element is set at an optimal value, when for instance the air conditioner switch is turned off after arriving at the optimal temperature, the operation of the compressor of the cooling unit is stopped and the air temperature in the automobile increases. In other words, there is a shortcoming in that the air temperature in the automobile is changed by ON-OFF operation of the air conditioner switch and the re-setting of the temperature setting element becomes necessary.